OrchidaceaeJuss.

Gen. Pl.: 64 (1789)nom. cons.

OrchidaceaeJuss.

Gen. Pl.: 64 (1789)nom. cons.

General Description

Perennial, terrestrial, saprophytic or epiphytic herbs or rarely scrambling climbers, with rhizomes, root-stem tuberoids or rootstocks with mycorrhizal fungi in the roots and often elsewhere.Growth either sympodial or less commonly monopodial.Stems usually leafy, but leaves often reduced to bract-like scales, one or more internodes at the base often swollen to form a "pseudobulb"; aerial, assimilating adventitious roots, often bearing one or more layers of dead cells called a velamen, are borne in epiphytic species.Leaves glabrous or occasionally hairy, entire except at the apex in some cases, alternate or occasionally opposite, often distichous, frequently fleshy and often terete or canaliculate, almost always with a basal sheath which frequently sheaths the stem, sometimes articulated at the base of the lamina and sometimes with a false petiole. Inflorescences erect to pendent, spicate, racemose or paniculate, one to many-flowered, basal, lateral or terminal, the flowers rarely secund or distichously arranged.Flowers small to large, often quite showy, hermaphrodite or rarely monoecious and polymorphic, sessile or variously pedicellate, most often twisted through 180 degrees, occasionally not twisted or twisted through 360 degrees.Ovary inferior, unilocular and the placentation parietal, or rarely trilocular and the placentation axile.Perianth epigynous, of two whorls of three segments; outer perianth whorl (sepals) usually free but sometimes variously adnate, the median (dorsal) often dissimilar to the laterals, the laterals sometimes adnate to the column foot to form a saccate, conical or spur-like mentum; inner whorl comprising two lateral petals and a median lip; petals free or rarely partly adnate to sepals, similar to sepals or not, often showy; lip entire, variously lobed or two or three-partite, ornamented or not with calli, ridges, hair cushions or crests, with or without a basal spur or nectary, margins entire to laciniate.Stylar and filamentous tissue forming a long or short column, with or without a basal foot, occasionally winged or with lobes or arms at apex or ventrally; anther one (or rarely two or three in extra African taxa), terminal or ventral on column, with a concave anther cap or opening by longitudinal slits; pollen in tetrads, agglutinated into discrete masses called pollinia; pollinia mealy, waxy or horny, sectile or not, 2, 4, 6 or 8, sessile or attached by caudicles, a stipes or stipites to one or two sticky viscidia; stigma 3-lobed, the mid-lobe often modified to form a rostellum, the other lobes either sunken on the ventral surface of the column behind the anther or with two lobes porrect.Fruit a capsule, opening laterally by 3 or 6 slits; seeds numerous, dust-like, lacking endosperm, sometimes markedly winged.

Notes: The classification of the family is currently the subject of some debate, particularly the number of subfamilies that should be recognised and the placement in those of certain tribes, subtribes and genera.The classification of the Orchidaceae outlined by Summerhayes (1968) in his account of the family for the Flora of East Tropical Africa differs in only relatively minor points from the most widely accepted of recent classifications (Dressler 1981, 1993).Summerhayes accepted three subfamilies; Apostasioideae, Cypripedioideae and Orchidoideae, dividing the last into four tribes; Orchideae, Neottieae, Epidendreae and Vandeae.All African orchids are placed in Summerhayes's Orchidoideae, neither the Apostasioideae nor the Cypripedioideae being represented in the continent.Dressler (1993) accepts five subfamilies: Apostasioideae, Cypripedioideae, Spiranthoideae, Orchidoideae and Epidendroideae, the last two equivalent more or less to the Orchideae and a combined Epidendreae and Vandeae of Summerhayes.The Neottieae of Summerhayes largely fall into Dressler's Spiranthoideae but Vanilla, Didymoplexis, Epipogium, Epipactis and Nervilia, all found in tropical Africa, are considered by Dressler to be primitive Epidendroideae.Dressler's 1993 classification is followed but the genera, except for the Spiranthoideae which precede the Orchidoideae here, are arranged more or less in the same order as in Summerhayes in the Flora of Tropical East Africa to facilitate comparison.

Notes: The classification of the Orchidaceae has been considerably revised since part 1 of the family was published in 1968. In particular, the division of the family into subfamilies and tribes has been considered in some detail by Dressler in the Proceedings of the 7th World Orchid Conference (1974) and in Selbyana (1979). In his latest treatment 6 subfamilies are recognised rather than the 3 accepted by Summerhayes for this Flora. The three additional subfamilies result from the division of the subfamily {i}Orchidoideae{/i} sensu Summerhayes into four subfamilies— {i}Orchidoideae{/i}, {i}Spiranthoideae{/i} Dressler, {i}Epidendroideae{/i} Lindl. and {i}Vandoideae{/i} Endl.All of these four subfamilies are represented in East Africa but they cannot be equated readily with the tribes of {i}Orchidoideae{/i} accepted by Summerhayes except for his {i}Orchideae{/i} which corresponds largely with the subfamily {i}Orchidoideae{/i} sensu Dressler. Dressler, however, has added the tribe {i}Neottieae{/i} to this subfamily as a result of removing the tribes {i}Cranichideae{/i} and {i}Erythrodeae{/i} from the {i}Neottioideae{/i} to a new subfamily {i}Spiranthoideae{/i}. He also removed from the {i}Neottioideae{/i} the tribes {i}Epipogeae{/i} and {i}Gastrodieae{/i} and placed them in the subfamily {i}Epidendroideae{/i} .If Summerhayes’ key to the tribes of the subfamily {i}Orchidoideae{/i} is followed, then the {i}Epidendreae{/i} will be seen to include not only the genera from {i}Vanilla{/i} to {i}Stolzia{/i} in this account, but also those up to and including {i}Neobenthamia{/i} in part 2 and {i}Eulophia{/i}, {i}Oeceoclades{/i}, {i}Pteroglossaspis{/i} and {i}Graphorkis{/i} in part 3. In most recent systems of classification, including that of Dressler (1979), the genera {i}Polystachya{/i} and {i}Neobenthamia{/i} have been included in the tribe {i}Polystachyeae{/i} and the genera {i}Ansellia{/i}, {i}Eulophia{/i}, {i}Oeceoclades{/i}, {i}Pteroglossaspis{/i} and {i}Graphorkis{/i} in the tribe {i}Cymbidieae{/i}, both of these tribes being included in the subfamily {i}Vandoideae{/i} along with the tribe {i}Vandeae{/i} of monopodial orchids.Thus, there are considerable differences between the classification used by Summerhayes (1968) and that advocated by Dressler (1979). Briefly, following Summerhayes, the genera are classified into tribes of the subfamily {i}Orchidoideae{/i} as follows:— {i}Orchideae{/i}, genera 1–17; {i}Neottieae{/i}, genera 18–25; {i}Epidendreae{/i}, genera 26–46; {i}Vandeae{/i} genus 47 onwards.In contrast, the genera would be classified into subfamilies as follows using Dressler’s system:— {i}Orchidoideae{/i}, genera 1–19; {i}Spiranthoideae{/i}, genera 20–25; {i}Epidendroideae{/i}, genera 26–39; {i}Vandoideae{/i}, genus 40 onwards.For the sake of consistency the key offered by Summerhayes to his tribes of the subfamily {i}Orchidoideae{/i} and his classification and arrangement of the genera is followed in parts 2 and 3. This in no way means that the present authors accept his classification but the convenience and the ease with which his key can be used militates against a revision of the classification at this late stage.

Perennial, terrestrial, saprophytic, epiphytic or very rarely subterranean or aquatic herbs or rarely scramblers, with rhizomes, tubers or rootstocks with mycorrhizal fungi in the roots and usually elsewhere. Growth usually sympodial, occasionally monopodial. Stems usually leafy, but leaves often reduced to bract-like sheathing scales, one or more internodes at or near the base frequently variously swollen into a “pseudobulb”; those of epiphytic species often bearing aerial assimilating roots protected from excessive heat and water-loss by layers of dead cells called the velamen. Leaves rarely hairy, undivided except at apex in some cases, alternate or very occasionally opposite, often distichous, frequently fleshy and often terete or canaliculate, almost always with a basal sheath which frequently surrounds the base of the peduncle, sometimes articulated at base of lamina and sometimes with a false petiole. Inflorescence spicate, racemose or paniculate, terminal and/or axillary, the flowers rarely secundly or distichously arranged, or flowers solitary. Flowers bracteate, hermaphrodite or very rarely polygamous or monoecious, zygomorphic, sessile or variously pedicellate, most often twisted through 180° (resupinate), occasionally not twisted or twisted through 360°. Perianth epigynous; perianth-segments 6, usually free but less frequently variously adnate, connate or adherent to one another or to the column, arranged in 2 whorls; both whorls similar or outer whorl (sepals) calyx-like and inner (petals) corolla-like, or outer whorl corolla-like and inner very reduced. Median segment of outer whorl (“dorsal” sepal) often different in size and shape from the 2 laterals, sometimes saccate or with 1 or 2 spurs. Median segment of inner whorl almost always markedly different from the 2 lateral segments. The segments of the outer whorl and 2 lateral segments of the inner whorl termed tepals, especially when basically similar in size, shape and colour. Median segment of inner whorl (lip or labellum) entire or variously lobed, frequently laciniate or fimbriate, often brightly coloured and frequently spotted or otherwise ornamented, often bearing crests (keels or carinae) along its length or with central portion (disk) or throat bearing a callus or cushion of hairs, often produced backwards into a sac or spur (rarely 2) up to 30 cm. long and sometimes with nectar at apex; often differentiated into 2 or 3 parts: basal part termed hypochile, often hinged to base of column or narrowed into a claw; middle part termed mesochile; apical part termed epichile. Stamens 1, 2 or 3, ± united with the style to form a special organ termed the column (gynostegium), apical part of which may be produced laterally into wings or vertically into stelidia, basal part often produced downwards to form a column-foot. Mentum or chin frequently formed from lateral sepals where tepals join column-foot. Anthers attached by their bases or apices, opening by a slit lengthwise or often operculate; pollen in distinct tetrads, sticky or agglutinated into 2, 4, 6 or 8 pollinia; pollinia mealy, waxy or horny masses, often divided into a number of smaller portions (sectile); at one end each pollinium occasionally drawn out into a sterile caudicle. Ovary inferior, 1-locular with 3 parietal placentas or rarely 3-locular with axile placentation, produced at the apex to form the column; very rarely apex of ovary with ring-like outgrowth (calyculus); ovules very small and numerous. Stigmas 3, fertile or more usually the 2 lateral ones fertile and the other transformed into an outgrowth (rostellum) lying between the anther and the lateral stigmas; part of the rostellum often modified into a sticky disk or disks called viscidia to which the pollinia are attached by 1 or 2 stalks (stipes) also derived from rostellum or by the sterile caudicle. The whole structure of pollinia, stipes or caudicle and viscidium form the pollinarium. Fruit a capsule opening laterally by 3 or 6 longitudinal slits. Seeds very numerous and small, without endosperm and with an undifferentiated embryo, often markedly winged.

Notes: Extensively grown as ornamentals, but of little other economic importance with the exception of Vanilla Mill, and the tubers of several species used as food.A perfectly satisfactory classification of the family into subfamilies, tribes and sub-tribes is not yet available although the publication of a new scheme is almost an annual event. The reader is referred to the excellent account by Dressier and Dodson, “Classification and Phylogeny in the Orchidaceae” in Ann. Miss. Bot. Gard. 47: 25 (1960) for a survey of the schemes to that date. These two authors also propose a reasonably practical system of classification of the orchids and stress that there are still many problems to be solved. Their paper helped to crystallize in our minds our ideas on this subject and the classification used in this account is the result.Our basic criterion is obviously overall similarity of floral and other morphological features but it must be remembered that this does not necessarily imply close relationships. A satisfactory classification must also be a usable one without undue multiplication of hierarchical categories, a state which visually results when it is attempted to apply absolute values to hierarchical levels of taxonomic similarity. We feel that the classification of a plant family should permit of easy translation into a curatorial system, and should be easy to remember. Consequently we use only those categories which nomenclaturally have a defined suffix and to which the rules of priority are readily applied.Many genera show a marked degree of interfertility both between their individual species and with species of other genera. This has given rise to innumerable artificial hybrids, both interspecific and intergeneric, which form the basis of a very important and extensive horticultural industry. At the generic level any insistence on interfertility criteria would be unwise but at the subtribal level we feel that all interfertile genera should be in the same subtribe. The considerable number of natural intergeneric hybrids and the enormous number of artificially produced commercial hybrids, often involving parentage from species of up to four genera in one plant, have contributed greatly to the knowledge of interfertility. Recent cytological work has also greatly clarified ideas at subtribal level.Three subfamilies are recognized by us. The Apostasioïdeae Garay (a very primitive and small group of Malesian plants) and the Cypripedioïdeae Garay (lady’s slipper orchids, widely cultivated and hybridized) do not occur in Africa and are characterized by the presence of two or three fertile anthers, the filaments arising below the level of the stigma. The Orchidoïdeae comprises over 98% of the family and normally has a single fertile anther, the filaments united with the style to form a distinct column. In the Orchidoïdeae, we recognize four tribes, all of which are represented in Africa and which may be distinguished by the following key. This part of the Flora deals with the tribe Orchidoïdeae only, the three remaining tribes being dealt with in the parts to follow.

Perennial, terrestrial, epiphytic or saprophytic herbs with rhizomes or tuberous roots or rootstock; stem leafy or scapose, frequently thickened at the base into pseudobulbs and bearing aerial assimilating roots. Leaves undivided, alternate and often distichous, rarely opposite, sometimes all reduced to scales, often fleshy, sheathing at the base. Flowers bracteate, hermaphrodite or very rarely polygamous or monoecious, zygomorphic; inflorescence spicate, racemose or paniculate, or flowers solitary. Perianth epigynous, composed of 6 petaloid segments (tepals) in 2 whorls, or the outer whorl calyx-like and the inner corolla-like, or the outer rarely corolla-like and the inner minute, free or variously connate in each whorl; outer segments (sepals) imbricate or subvalvate, the middle segments of each whorl generally different in size and colour from the lateral ones, especially the middle petal which is often extremely complicated in structure and is termed the lip or labellum; the basal part of the labellum, the hypochile, is often articulated to the base of the column or is much constricted, when it is termed the claw; the middle part, the mesochile and the apical part, the epichile, may be variously lobed and often bear outgrowths. On account of the twisting of the ovary through 180°, the labellum is often placed in an abaxial position; frequently the labellum or more rarely the odd sepal is prolonged into a sac or spur, sometimes very long. Stamens 2 or 1; stamens and style united to form a special structure (column), the apex of which may be produced vertically into stelidia or laterally into wings, and the base of which may be produced downwards to form a foot; anther or anthers 2-locular, introrse, opening by a slit lengthwise; often operculate, i.e. can be lifted like a little cap; pollen granular or generally agglutinated into mealy, waxy or bony masses (pollinia); at one end the pollinium may be extended into a sterile portion (caudicle); the pollinia may be free in the anther-loculi or more or less loosely united. Ovary inferior, 1-locular with 3 parietal placentas or very rarely 3-locular with axile placentas, usually produced at the apex to form the column; stigmas 3 fertile, or more frequently the lateral 2 fertile, the other sterile and transformed into a small outgrowth (rostellum) which lies between the anther and the stigmas; a portion of the rostellum is sometimes modified into a viscid disk or disks (viscidia) to which the pollinia are attached, often by a stalk or stipes. Ovules very numerous and minute. Fruit usually a capsule, mostly opening laterally by 3 or 6 longitudinal slits. Seeds very numerous, minute, often drawn out at each end, or rarely winged, without endosperm; embryo not differentiated.

Perennial, terrestrial, epiphytic or lithophytic herbs or rarely scrambling climbers, sometimes saprophytic. Mycorrhizal fungi in the roots and often elsewhere. Growth either monopodial or more commonly sym-podial with rhizomes, tubers, or rootstocks. Roots adventitious, often aerial, sometimes assimilatory, with velamen tissue in epiphytic and some terrestrial species. Stems usually leafy, the one or more inter-nodes often swollen in sympodial species to form pseudobulbs. Leaves glabrous or occasionally hairy; usually entire, rarely palmate or lobed; alternate or occasionally opposite, often distichous, with plicate or convolute vernation; membranaceous to coriaceous, often terete or canaliculate, reduced to scale-like bracts in some species; almost always with a basal sheath, sometimes articulated at the base of the lamina or with a false petiole. Inflorescences erect to pendent; spicate, racemose or paniculate; one- to many-flowered; basal, lateral or terminal, the flowers rarely secund, distichous or subumbellate. Flowers small to large, often showy; zygomorphic but appearing almost actinomorphic in some cases; bisexual or rarely unisexual and polymorphic; sessile or variously pedicellate, most often twisted through 180°, occasionally not twisted or twisted through 360°. Sepals three, usually free but sometimes variously connate, the dorsal sepal often dissimilar to the lateral sepals, the lateral sepals sometimes adnate to the column foot to form a saccate, conical or spur-like mentum. Petals three, free or rarely adnate in part to the sepals, the medial petal distinguished from the others as the lip or labellum. Lip entire, variously lobed or two- or three-partite, often ornamented with calli, ridges, hair cushions or crests, with or without a basal spur or nectary, margins entire to laciniate. Column short to long, formed from stylar and filamentous tissue, with or without a basal foot, occasionally winged or with lobes or arms apically or ventrally; fertile anthers one (rarely two or three), terminal or incumbent, cap-like or dehiscing by longitudinal slits; pollen shed as monads or tetrads, often agglutinated into discrete masses called pollinia; pollinia mealy, waxy or horny, soft to hard, sectile or not, 2, 4, 6 or 8, sessile or attached by caudicles or stipites (tegula or hamulus) to one or two sticky viscidia forming a pollinarium; stigma 3-lobed, the midlobe often modified to form a rostellum, the other lobes either sunken on the ventral surface of the column behind the anther or with two lobes porrect. Ovary inferior, unilocular with parietal placentation or rarely trilocular with axile placentation. Fruit a capsule, usually opening laterally by three or six slits, rarely baccate; seeds numerous, dust-like, rarely with hard seed coats, lacking endosperm, sometimes markedly winged.

Distribution

Orchidaceae comprise one of the largest families of flowering plants, with an estimated 800 genera and conservatively almost 20 000 species (Atwood 1986; Dressier 1993). They are distributed throughout all continents except Antarctica but are most numerous in the humid tropics and subtropics.

Uses

Hundreds of species are grown throughout the world as ornamentals. Two or possibly three species of Vanilla Miller are grown commercially to produce the flavouring vanillin. Tubers of several species are used for food or aphrodisiacs; various plant parts of other species are used in folk medicine, particularly in India, China, the Far East, Africa, and Madagascar (Lawler 1984).

WCSP 2014. 'World Checklist of Selected Plant Families. Facilitated by the Royal Botanic Gardens, Kew. Published on the Internet; http://apps.kew.org/wcsp/ Retrieved 2011 onwards

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